1. Field of the Invention
This invention relates to the art of MAG welding, and more particularly, to a solid wire for MAG welding which has no copper plating on the wire surface and which has good welding workabilities such as a reduced amount of generated spatters and good arc stability in the MAG welding of steel sheets (such as mild steel and 490 N/mm.sup.2 grade high tension steel sheets).
2. Description of the Prior Art
The term "MAG welding (metal active gas welding)" used herein is intended to mean arc welding wherein a welding wire, which is consumed as a welded metal, is used as an electrode, a mixed gas (e.g., 80% Ar+20% CO.sub.2) composed of argon gas to which carbon dioxide or oxygen is added at a mixing rate of the oxidative gas of 10 to 30% is used as a shield gas, and the particle transfer proceeds as a spray transfer and so-called carbon dioxide welding is not included herein.
As a solid wire for such MAG welding as mentioned above, it is usual to use a so-called copper-plated solid wire wherein copper is plated on the wire surface. The reason why copper is plated is to improve electric conductivity and a corrosion resistance.
We have observed an arc phenomenon of MAG welding by use of a video camera for high speed recording and reproduction (capable of taking 2000 frames per second). As a result, it has been found that with copper-plated solid wires, the surface tension of transfer particles released and separated from the wire tip is smaller than that attained by a wire having no copper plating thereon. In fact, the particles are not in a spherical form, but in the form of an ellipsoid elongated toward the transfer direction (i.e. a dropping direction) (see FIG. 3). This may cause an instantaneous short-circuiting phenomenon wherein particles being transferred from the wire tip to a melt pool of a base metal are connected to one another to cause short-circuiting for a very short time. Eventually, once connected particles are broken into pieces and scattered to cause spatter generation.
When using a copper-plated solid wire in long-time welding such, for example, as by a welding robotic system, the wire is rubbed within an elongated conduit tube (or conduit liner) guiding a wire from a wire feeder to a welding torch body. As a consequence, copper dust is accumulated in the tube, thereby causing an arc to become unstable owing to the failure in the feed of the wire. This leads to the disadvantage that the tip of the wire is run into the melt pool, thereby causing the spatter generation.